Metallocene-type complexes are increasingly becoming important as a new generation of catalysts for the preparation of polyolefins. By metallocenes, it is understood transition metal complexes containing one or more π ligands of the cyclopentadienyl type, substituted or not, such as, for example, sandwich- or half-sandwich-type compounds, i.e., metal complexed to two π ligands or one π ligand, respectively. These complexes become active in olefin polymerization when activated by an organometallic compound also known as cocatalyst. Known examples of cocatalysts, widely used in the activation of metallocenes, are aluminoxanes, particularly methylaluminoxane (herein referred as MAO).
Comparatively to the conventional Ziegler-Natta catalytic system, the homogeneous metallocene catalytic systems not only show high catalytic activities, but also the capacity to control the properties of the polyolefins as function of the compounds used in its synthesis and reaction conditions.
A great number of publications related to the preparation of polyolefins with metallocenes are appearing in literature. However, the disadvantage, in most cases, is the fact to be required the use of a large excess of aluminoxanes, in relation to the transition metal content of the catalyst, to yield acceptable productivities. Due to the high cost of the aluminoxane and also to the necessity of extra work of purification of the polymers obtained, the production of poliolefins in industrial scale, based on these catalytic systems, generally becomes anti-economic. Besides, the use of toluene, which is commonly used in the formulation of aluminoxanes solution, particularly the MAO, is increasingly becoming highly undesirable due to toxicological reasons in relation to the field of application of the polyolefins and storage stability reasons of the highly concentrated formulations (tendency to gel formation).
Efforts have been made in the sense to substitute, at least partially, the use of aluminoxanes for lower cost compounds or those having less adverse effects in the productivity, morphology and properties of the polymers. Such efforts are shown in the patents EP-A 287666, EP-A 294942, EP-A 442725, EP-A 553757 and WO 97/11775.
According to Ishihara in his article Macromolecules 21, 3356 (1988), metallocene catalysts with monocyclopentadienyl ligand such as, for example, CpTiCl3, after reacting with MAO, are effective in the polymerization of styrene obtaining high yields of syndiotactic polystyrene. However, Chien had demonstrated in his article, J. Polym. Sci., Polym. Chem. Ed. 28, 15 (1990), that the CpTiCl3-MAO complex has very low activity for ethylene polymerization.
Other known problem of the use of metallocene catalysts are the “poor” morphology of the polymeric material obtained; this results in apparent low bulk density and heterogeneous polymer. Since the replication phenomenon is being applied to polymerization reactions, i.e., the formation of polymer particles with morphology similar to those of catalyst particles, the problem has been resolved only improving the morphology of the catalyst used on those reactions. Methods for producing supported metallocene catalysts are described, for example, in the patents WO 95/07939, WO 87/03889, WO 94/28034, EP 206794 and EP 250600, where derivatives of aluminoxane compounds are used as cocatalysts. In addition to aluminoxane compounds, organoboron based compounds can also be used as activators, and the patents WO 91/09882, WO 94/03506, EP 628574 and WO 95/15815 teach to use them along with metallocene catalysts during the supported catalyst preparation.
The Chinese patent CN 1364817A, in its turn, shows that it is possible to obtain polyethylene from a silica-based supported metallocene catalyst containing monocyclopentadienyl and β-dicetone ligands, magnesium chloride and activated by MAO.
Several catalytic systems have been used to produce polyethylenes presenting an extremely high molecular weight. Such polymers are usually known as ethylene homopolymer or ethylene copolymer with α-olefins, of high and ultra high molecular weights, called henceforth HMWPE and UHMWPE, respectively. The HMWPE shows viscosimetric molecular weight (herein referred as Mv) that may range between 500,000 to 2,500,000 g/mol, while the UHMWPE shows Mv that is above 2,500,000 g/mol, which represents about 10 to 20 times more than the molecular weight of conventional high-density polyethylene (herein referred as HDPE).
The U.S. Pat. No. 5,576,600 teaches how to prepare a UHMWPE with a Ziegler-Natta catalyst and also shows that α-olefins, such as butene-1, which can be incorporated in these polyethylenes.
The commercially produced UHMWPE in moderate pressures and temperatures is traditionally obtained by Ziegler-Natta catalyst, as showed in patents U.S. Pat. No. 5,880,055 and BR 9,203,645A. Another characteristic of these polymers is that they show similar property to the conventional HDPE that is the broad molecular weight distribution (herein referred as MWD), with the MWD value ranging from 5 to 20.
Highly active metallocene catalysts as any single-site type catalyst for HMWPE and UHMWPE synthesis are not very common. For example, the U.S. Pat. No. 5,444,145 teaches how to prepare polyethylene presenting ponderal average molecular weight (herein referred as Mw) until 1,000,000 g/mol and containing incorporated α-olefins, with a homogeneous metallocene catalyst. Such polyethylenes show narrow MWD and a homogeneous distribution of α-olefin in the polyethylene chain. Moreover, the U.S. Pat. No. 6,265,504, in its turn, teaches how to produce a polyethylene with Mw higher than 3,000,000 g/mol and a MWD below 5 with single-site type catalyst, which is an organometallic compound containing a ligand with heteroatom, and activated by non-aluminoxane compounds. Other single-site catalysts containing ligands as pyridine are reported in the U.S. Pat. No. 5,637,660 and are particularly useful to produce UHMWPE with Mw above 3,000,000 g/mol.
Recently, in patent WO 02/079272, the synthesis of a homogeneous metallocene catalyst with bisindenil ligands with double bridge between these ligands which produced a polyethylene with Mw between 500,000 e 10,000,000 g/mol, was reported.
The U.S. Pat. No. 6,265,504 comments that the patent processes include solution, slurry and gas-phase, but the preference is by the process in solution. U.S. Pat. No. 5,444,145, in its turn, comments that the catalyst can be used in polymerization processes using liquid phase for synthesis.
Therefore, references in the state of the art, considered alone or in combination, do not describe nor suggest a process for the preparation of supported metallocene catalysts for the reaction of ethylene homopolymerization and ethylene copolymerization with α-olefins from supported metallocene catalysts based on transition metals of the groups 4 or 5 of the periodic table, containing ligands like monocyclopentadienyl, monoindenyl or monofluorenyl, substituted or not, in the absence of activators such as aluminoxanes or organoboron compounds and that produce ethylene homopolymers and ethylene copolymers with α-olefins, with high molecular weight and ultra high molecular weight, such as HMWPE and UHMWPE, with broad molecular weight distribution, used in gas-phase and bulk polymerization processes in addition to processes in slurry, as described and claimed in this application
The obtained ethylene homopolymers and ethylene copolymers with α-olefins show high molecular weight, broad MWD, in the presence of mentioned supported metallocene catalysts based on transition metal of the groups 4 or 5 of the periodic table, containing ligands like monocyclopentadienyl, monoindenyl or monofluorenyl, substituted or not. More specifically, the present invention relates to a process for preparation of supported metallocene catalysts based on transition metal of the groups 4 or 5 of the periodic table, containing ligands like monocyclopentadienyl, monoindenyl or monofluorenyl, substituted or not, for the reaction of ethylene homopolymerization and ethylene copolymerization with α-olefins, from a catalytic support prepared in the absence of activators such as aluminoxanes or organoboron based compounds. More specifically, the present invention also relates to a process to produce ethylene homopolymers or ethylene copolymers with α-olefins, with high molecular weight and ultra high molecular weight, such as HMWPE and UHMWPE, with broad MWD, in the presence of the mentioned supported metallocene catalysts based on transition metal of the groups 4 or 5 of the periodic table, containing ligands like monocyclopentadienyl, monoindenyl or monofluorenyl, substituted or not, in the absence of activators like aluminoxanes or organoboron based compounds. The invention also relates to the catalytic support prepared in the absence of activators such as aluminoxanes or organoboron based compounds, to the supported metallocene catalysts based on transition metal of the groups 4 or 5 of the periodic table, containing ligands like monocyclopentadienyl, monoindenyl or monofluorenyl, substituted or not, to the ethylene homopolymers and ethylene copolymers with α-olefins, with high molecular weight and ultra high molecular weight, such as HMWPE and UHMWPE, and broad MWD, and to the polymerization processes to produce ethylene homopolymers and ethylene copolymers with α-olefins with high molecular weight and ultra high molecular weight in presence of the mentioned supported metallocene catalysts based on transition metal of the groups 4 or 5 of the periodic table, containing ligands like monocyclopentadienyl, monoindenyl or monofluorenyl, substituted or not, and in the absence of activators such as aluminoxanes or organoboron based compounds.